The present invention relates to a wheel which is formed of a wheel disk and of a monobloc mounting rim for a tire, preferably a tire which has a radial carcass reinforcement and is capable of possibly forming, with a tread supporting ring in said tire, a rolling assembly which may be useful in the event of travel when the inflation pressure drops abnormally as compared with the normal pressure of use, known as the nominal service pressure, which pressure may even be zero.
The main difficulties encountered in the case of traveling on a flat tire or a tire with low pressure concern the risk of separation of the bead of the tire and, in particular, separation of the bead located on the outer side of the tire mounted on the outer side of the vehicle. The well-known techniques proposed for avoiding such separations, and in particular the one consisting of arranging a protrusion or hump of small height axially to the interior of the rim outer seat, do not appear to give full satisfaction and tend to increase the difficulties in the mounting and dismounting of the tires.
French Application No. 2 699 121 describes, by way of example, a monobloc wheel rim 1 shown in FIG. 1 for the effective solution of the above problem. Said rim 1 is limited axially by two rim edges spaced axially apart by the width S of the rim. Said rim 1 comprises, as viewed in meridian section:
a first rim seat 13' having a generatrix the axially outer end of which is on a circle of a diameter less than the diameter of the circle on which the axially inner end is located (the seat is then said to be inclined towards the outside) and limited axially to the outside by a protrusion or hump 15' of slight height; PA1 a second rim seat 13" having a generatrix the axially inner end of which is, on the one hand, on a circle of a diameter at least equal to the diameter of the circle on which the axially inner end of the generatrix of the first rim seat is located (and in the case shown in FIG. 1 of said application, on a circle of a diameter equal to that on which the axially inner end is located) and, on the other hand, on a circle of a diameter greater than the diameter of the circle on which its axially outer end is located, said second generatrix being extended axially to the outside by a hump 15" and axially to the inside by a rim flange 14.
In accordance with the respective differences in diameter of the circles on which the axially inner ends of the two rim seats are located, said rim may or may not be provided with a mounting groove 12, preferably located axially close to the second rim seat 13".
Said rim 1 is intended to be used advantageously with a tread support (not shown), a resilient support which can be removed and placed on a rim bearing surface 11, the generatrix of which may be linear or not and, if linear, parallel or not to the axis of rotation, a positioning stop 16 located between said bearing surface 11 and the mounting groove 12 permitting the axial positioning of the support in collaboration with one of the beads of the tire.
The depth of the mounting groove as well as the operating constraints which are not to be exceeded make necessary, in case the wheel is made of steel and the desired radially outer profile being given, axially variable thicknesses of metal and thus a radially inner meridian profile such as that shown in FIG. 1. It follows from an examination of said figure, and this in practically all possible mountings of tires on rims of this type, that the space radially available below the mounting groove 12 is greatly reduced as compared with the space radially below the bearing surface 11.
The fact that the mounting groove is situated axially closer to one edge of the rim than to the middle of the surface entails the risk of leading to the accumulation, below the corresponding portion of the bearing surface, of all sorts of materials, such as mud mixed to a greater or lesser extent with particles, such as snow or ice under winter conditions, which materials are difficult to remove. Furthermore, the constant desire for less weight of the rim leads to the use of a material of low density for its manufacture. This use permits production in the form of a wheel, rim 1 and disk being then molded together at the same time but, on the other hand, results in serious modifications of the radially inner and outer meridian profiles, respectively, so as to correctly stabilize said wheel, in view of the severe conditions imposed by travel under zero or low pressure.